AVS 61st International Symposium & Exhibition
    Surface Science Wednesday Sessions
       Session SS-WeA

Paper SS-WeA9
Low-Temperature STM Observation of Asymmetrical Adsorption and Chirality of Ga Adatoms on Wurtzite GaN(000-1 )

Wednesday, November 12, 2014, 5:00 pm, Room 309

Session: Chirality and Enantioselectivity on Surfaces
Presenter: Khan Alam, Ohio University
Authors: K. Alam, Ohio University
A. Foley, Ohio University
J. Corbett, Ohio University
Y. Ma, Ohio University
J. Pak, Ohio University
A.R. Smith, Ohio University
Correspondent: Click to Email
A sample with atomically flat terraces having the c(6×12) reconstruction on GaN(000-1) surface is grown by molecular beam epitaxy and studied at liquid helium temperature using scanning tunneling microscopy. Being the most Ga-rich reconstruction (corresponding to the Ga stability limit) occurring on the N-polar GaN surface,[1] low-temperature STM imaging reveals new details of the c(6×12), although not inconsistent with the early model.[2] Unexpectedly however, a dilute concentration (0.0031 ML) of single atomic adsorbates not seen at room temperature is found covering the terraces. The coverage is stable with time and increases with Ga flux during growth. These adsorbate features are thus attributed to the condensation of Ga adatoms which at room temperature would be in a 2D gas-like state at the surface. Surprisingly, the Ga adsorbates manifest at ~+2.5 V sample bias as distinct L-shapes which are always in one of two possible orientations with respect to <10-10>. Furthermore, on any given atomic terrace, the probability of finding one of the two L-shape orientations is 80%, reversing across a step. However, no in-plane rotation will result in the opposite handed-ness of an L-shape, on either terrace. The L-shaped adsorbates thus reveal broken chiral symmetry linked to adsorption probability, which is attributed to symmetry breaking of the c(6×12) reconstruction.